Title: Respiratory responses of a subarctic biocrust from the highlands of Iceland to experimental warming: Comparison between a dry and a wet summer

Understanding the response of biocrust respiration to warming is crucial for terrestrial carbon cycle simulation in high north ecosystems. Biocrust respiration is sensitive to warming which could result in positive carbon-climate feedback. However, evidence on the sensitivity of biocrust respiration to warming is mostly from arid and semi-arid ecosystems. To assess how subarctic biocrust responds to warming, a field experiment was undertaken to study the effect of experimental warming on the respiratory responses of subarctic biocrust under different soil moisture conditions. Warming plots simulated by using Open Top Chambers (OTCs), and plots of ambient environment (control) were established. A LICOR-6400 and an EGM-5 portable gas analyser were used to measure soil respiration rates in June of two different years, 2019 and 2022, corresponding to dry and wet moisture conditions respectively. Soil moisture and temperature were also measured from the plots, simultaneously with soil respiration, using probes attached to the portable gas analysers. There was no effect of warming on soil moisture content under the different moisture conditions of dry and wet. Soil temperature increased by 1.2^oC, corresponding to a 9.8% increase in the OTCs in relation to the control plots only under drier conditions. Under wet conditions, warming had no effect on the soil respiration rate. However, the effect of warming on soil respiration rate was negative under drier conditions. The results of this study showed that the effects of warming on the respiration of subarctic biocrust largely depends on moisture conditions.